Effect of synthesis method on the structure and properties of perovskite NaNbO3 type nanomaterials

Ferroelectric nanostructures have attracted much attention recently due to the ongoing demand for miniaturization of devices and discover new phenomena. One of the materials studied intensively in recent years is potassium niobates with perovskite structure is a promising material for electro-optic, nonlinear optical, and photorefractive applications such as frequency doubling, wave guiding, and holographic storage. The structure and morphology of NaNbO3 perovskites are studied in the context of their possible use for sensors application. Materials are prepared by hydrothermal, sol-gel and ultrasonic method using different thermal treatments. Powders obtained were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR)

Substitution effect on the physico-chemical properties in crednerite CuMnO2 type materials

Recently, the ABO2 delafossite-type class of materials, B being a transition element, has attracted a lot of interest. First of all in the field of transparent conducting oxides, thin films of CuAlO2 show the unusual combination of high transparency and rather high p-type semi-conductivity [1]. On the other hand, in the field of the exotic magnetic and structural properties, a good example is the CuFeO2 delafossite, a triangular lattice antiferromagnet which has been extensively studied over the last years for its multiferroïcity [2,3]. The ABO2 delafossite structure, where A=Cu and Ag, and B a transition element, belongs to the R-3m space group and is characterised by O-Cu-O dumbells linking layers of edge sharing BO6 octahedra. However, in this class of materials,crednerite CuMnO2occupies a unique placedue to the Jahn-Teller (JT) distortion of the Mn3+ (t2g 3 eg) which leads to a monoclinic structure (C2/m space group at room temperature) and to a different topology of the magnetic triangular lattice and out-of-plane stacking sequence compared to delafossite structure. In this work, we investigated the physico-chemical properties of CuMn1-XBXO2 (B=Al, Mg; x=0 - 0.08) type materials by X-Ray diffraction, SEM-EDAX, thermal analysis, UV-VIS and infrared spectroscopy. The effect of the substitution on the lattice parameter in CuMnO2is significant in order to understand the correlation between the structure and the properties in this compound.The crednerite nanoparticles were synthesized at low temperature by hydrothermal method in teflonlined steel autoclave

Mg substitution in CuCrO2 delafossite compounds

A detailed investigation of the series CuCr(1-x)MgxO2 (x = 0.0 - 0.05) has been performed by making high-temperature resistivity and thermopower measurements, and by performing a theoretical analysis of the latter. Microstructure characterization has been carried out as well. Upon Mg2+ for Cr3+ substitution, a concomitant decrease in the electrical resistivity and thermopower values is found, up to x ~ 0.02 - 0.03, indicating a low solubility limit of Mg in the structure. This result is corroborated by scanning electron microscopy observations, showing the presence of MgCr2O4 spinels as soon as x = 0.005. The thermopower is discussed in the temperature-independent correlation functions ratio approximation as based on the Kubo formalism, and the dependence of the effective charge carrier density on the nominal Mg substitution rate is addressed. This leads to a solubility limit of 1.1% Mg in the delafossite, confirmed by energy dispersive X-ray spectroscopy analysis.Comment: 6 pages, 5 figure

Structural and optical properties of layered ammonium-iron (II) phosphate monohydrate

Ammonium-iron phosphates phases have recently attracted more interest due to their promising applications as fertilizer [1] or as promising anode material for lithium-ion battery application [2], for example. In this context, NH4FePO4·H2O materials are obtained from FeCl2, Fe2O3 and NH4H2PO4 as starting reagents and NH4OH solution by one step hydrothermal method. The factors that affect the formation processes and the product morphologies: the pH and reaction time have been analysed. The as-synthesized compounds have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier Transform infrared (FT-IR) spectroscopy. The optical properties of NH4FePO4·H2O were for the first time studied in this research work: the material displays ptype conductivity behaviour and the value for direct optical band gap EG is estimated to be approximately ~3.6 eV. The results from this paper suggests that these phosphate materials could be suitable candidates for several applications as for example in photovoltaic technology

Electrochemical behaviour of LaMnO3-modified graphite electrodes

The electrochemical behaviour of LaMnO3-modified graphite electrodes was studied using cyclic voltammetry. Potassium ferricyanide was employed as a probe to determine the electroactive surface area of LaMnO3 modified electrodes and their diffusion coefficient. The electroactive surface area and the diffusion coefficient were calculated using the RandlesSevcik equation

Impact of dopants on the electrical properties in ABO3 perovskite type materials

The ceramics materials with ABO3 structure based on iron or silver doped sodium tantalate, were successfully synthesized using the ultrasonically method with immersed sonotrode in the reaction medium followed by heat treatment at 600°C. Samples were doped with silver for the A site of the perovskite lattice and with iron for the B site. The doping was performed in order to improve the electrical properties through change the crystalline structure and prevent ordering of the oxygen vacancies in these materials. The obtained materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), BET analysis, energy-dispersive Xray spectroscopy (EDX) and electrical measurements. Structural analysis shows that the obtained materials have cubic structure and a homogeneous composition, without secondary compounds. Electrical measurements indicate that the presence of metal ions of iron or silver in the structure of NaTaO3 lead to decreases of the gap band energy, resulting in increase of electric conductivity

Analysis of the crystalline structure and morphological features of perovskite materials performed through different ways

Manganites are mixed oxides of manganese whose broad stoichiometric formula is ABO3, where A is a lanthanide element and B is manganese, with possible oxygen nonstoichiometry. Usually the manganite compounds crystallize within perovskite structure, with the following possible space groups: ideal cubic structure Pm3m, orthorhombic Pbnm or rhombohedral R3CH [1, 2]. The phase purity and physico-chemical properties of perovskites depends upon the preparation methods, thus a variety of chemical methods have been developed to prepare lanthanum manganite nanoparticles at low cost and lower processing temperature [3]. In order to analyze the crystalline structure and morphological properties, LaMnO3 materials were prepared by ultrasonic method with immersed sonotrode in the reaction medium (US) and the sol-gel technique (SG), followed by thermal treatment at low temperature. Structural characterization was performed by X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR), and morphological analysis was achieved using atomic force microscopy (AFM) and trasmission electron microscopy (TEM)